1. Field of the Invention
The present invention relates to a monitor system for hydraulic pressure circuits of vehicles, and more particularly to the monitor system for monitoring a hydraulic braking pressure in each hydraulic pressure circuit including a wheel brake cylinder of an automotive vehicle which has a hydraulic pressure control apparatus for supplying the hydraulic braking pressure into the wheel brake cylinder through the hydraulic pressure circuit in response to depression of a brake pedal.
2. Description of the Related Arts
In general, a vehicle is provided with a braking system for supplying a hydraulic braking pressure into each wheel brake cylinder in accordance with the depressed amount of a brake pedal, i.e., the brake pedal stroke. However, a desired hydraulic braking pressure may not be supplied constantly, due to a vapour-lock or the like.
In a Japanese Patent Laid-open Publication No. 4-56668, for example, a brake pedal stroke compensating apparatus has been proposed to compensate a hydraulic pressure corresponding to the brake pedal stroke. The apparatus includes means for measuring the brake pedal stroke, means for detecting the hydraulic pressure in a main hydraulic passage, and a fluid supply apparatus which compares a signal output from the stroke measuring means with a signal output from the pressure detecting means to calculate an amount of fluid lacking in the main passage and supply the lacking amount of fluid into the main passage.
However, it is not easy to determine a lack of the hydraulic braking pressure supplied to each wheel brake cylinder. Therefore, generally employed is means for directly detecting the hydraulic pressure generated from a master cylinder, as proposed previously. Since a pressure sensor for detecting the hydraulic pressure is relatively expensive, it is desired to determine without using the pressure sensor at least such a condition that a proper hydraulic braking pressure is applied to each wheel brake cylinder.
According to the apparatus as described above, it is possible to determine the condition of the hydraulic braking pressure in a braking system as a whole by detecting the hydraulic pressure generated from the master cylinder. However, it is impossible to determine the condition of the hydraulic braking pressure in each hydraulic pressure circuit including a wheel brake cylinder provided for each wheel.